Stabilized control circuit



June 10, 1952 5, w, NAGEL 2,600,317

STABILIZED CONTROL CIRCUIT Filed March 18, 1950' WITNESSES: INVENTORGeor eW.Nc| el. x51 BY 9 g I ATTORNEY Patented June 10, 1952 STABILIZEDCONTROL CIRCUIT George W. Nagel, Pittsburgh, Pa., assignor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Application March 18, 1950, Serial No. 150,443

6 Claims. 1

My invention relates to an electron discharge circuit and especially toa circuit for stabilizin an electron valve.

Conventional relay circuits frequently include a relay actuating coilconnected in series with a grid-controlled gas-discharge type ofelectron valve. Since conduction through this type of tube cannot beinterrupted by manipulation of the potential of its control grid, it isconventional to use an alternating voltage source for the anode-cathodepotential. This effectively interrupts the current flow every cycle andthus restores eiiectiveness to the control grid.

This procedure necessarily means that the supple of energy to the relaycircuit is intermittent. To avoid relay chattering, it is conventionalto shunt a capacitor across the relay coil. The capacitor stores energyduring the conductive portion of each cycle and discharges through therelay coil during the remainder of the cycle to cause the coil to remainactuated during the full cycle of the alternating current. A controlvoltage is impressed on the grid of the valve to cause it to becomeconductive. This control voltage gradually becomes more positive withrespect to the cathode of the valve until a point is reached at whichthe control voltage causes the valve to become conductive. Current thenflows through the relay coil.

In the usual arrangement, this control voltage increases graduallyuntil, during some one positive half-cycle of the source voltage, thevoltage impressed on the grid of the valve is just sufficient to causethe valve to become conductive when peak value of the source potentialis impressed I from cathode to anode on the valve.

I have found that in such a control circuit the valve becomesconductive, actuating the relay for one cycle, but the valve does notbecome conductive during the next succeeding half cycles. This causesthe relay to close momentarily and open, remaining open for a fewcycles. This 0peration is referred to as chattering or the relay. Relaychattering is a highly objectionable phenomenon.

In some circuit arrangements the control circuit is capable ofimpressing only a limited voltage on the control grid of the thyratron.Such a control circuit may be capable of starting conduction in thethyratron when the full voltage of the source is impressed across thethyratron but may be incapable of starting the thyratron when a slightlylower voltage is impressed on it.

A similar problem arises in the use of a coldcathode gaseous-dischargevalve. Conduction in such a valve is initiated by a glow dischargebetween the control electrode and the cathode. The magnitude of thecurrent required in this discharge to cause the initiation ofanode-cathode conduction in the valve is dependent upon the voltageimpressed on the anode of the valve. A circuit may be inoperative if thecurrent available from the control circuit is limited to a value belowthat required to initiate discharge in the valve.

An example of a circuit which may at times be subject to such adifficulty is shown in the application of Schultz and Nagel, No. 12,038, filed February 28, 1948, entitled Garage Door Opener" and whichhas become abandoned. The circuit shown in Fig. 3 of this applicationincludes a cold-cathode gaseous-discharge valve 29 which is started bycurrent flow from the photoelectric cell 4. The relay 28, connected tothe valve 29, is shown symbolically as a winding. Such windingsgenerally have a shunting capacitor to maintain the relay actuatedduring the negative halfcycle. The photo cell 4 must provide a currentgreater than a certain predetermined minimum if the valve 29 is tobecome conductive. After the first period of conduction, the relaycircuit connected to the anode of the valve 29 impresses a back voltageon the valve and then a greater current flow is required between thegrid 46 and the cathode of valve 29 to initiate conduction during thenext positive half-cycle. Under some circumstances, the light whichimpinges on the photo cell 4 and the characteristics of the photo cell 4may be such that the current from photo cell 4 is sufficient to initiateconduction in valve 29 for one cycle but is insufilcient to initiateconduction during succeeding positive half-cycles. Thus the currentrequired to fire the valve 29 is dependent upon its past history ofconduction, i. e. a current which will cause conduction in a cycle aftera non-conductive cycle may be insufilcient to fire the valve during acycle which follows a conductive cycle.

Accordingly, it is an object of my invention to provide a circuit for agaseous discharge valve which allows the discharge valve to be equallyresponsive to a control regardless of its past history of conduction.

It is an object of my invention to provide a relay control circuit whichwill operate in response to a gradually changing control voltage butwill not cause chattering of the relay.

It is a further object of my invention to provide a stabilizing systemwhich maintains substantially infinite the transconductance of agridcontrolled electron discharge device.

It is a further object of my invention to provide a circuit for agrid-controlled electron discharge device which will maintain constantits circuit response to a control voltage.

My invention arises from the realization that this chattering of therelay is due to a decrease in the voltage impressed across the valveafter a first conductive period due to the presence of a residualsubtractive potential across a capacitor in its anode circuit. Thiseffect varies the control potential and/or current re'qui'red toinitiate conduction of the valve during succeeding cycles and thereforechanges its response to the control voltage.

The critical voltage which will cause the valve to become conductive isdependent upon the characteristics of the valve and upon the anode tocathode voltage impressed on the valve. The valve becomes conductingpassing current through the relay coil and the capacitor associated withthe coil. 'During the following negative half-cycle of the sourcevoltage the capacitor partially discharges through the relay coil.During'the next positive half-cycle, the capacitor is not completelydischarged and it effectively reduces the anode to cathode voltageimpressed on the valve below the peak value of the source potential. Ifthe control voltage has increased only slightly or not at all since theprevious half-cycle, it is not now great enough to cause the valve tobecome conductive when a voltage less than the peak value f the sourcevoltage is impressedon the'valve. Thus, in normal operations ofconventional relay circuits, the control circuit may cause the valve tobecome conductive during part of one positive half-cycle of the sourcepotential but be unable to cause the valve to become conductivein thenext one or more positive half.- cycles. The relay may, thereforeQbereleased afterhaving been actuated and a chattering of the relay mayoccur as it closes andopens repeatedly.

In accordance with my invention I provide a circuit in which the voltageimpressed on the relay coil is derived from a resistor connectedinseries with a control thyratron. A rectifier connected in series withthe relay coil prevents the voltage' across the relay coil fromaffecting the operation of the control thyratron prior to conduction.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of a specificembodiment when read in connection with the accompanying drawing, thefigure of which is a schematic diagram showing a preferred embodiment ofmy invention.

As shown in the drawing, a thyratron 3 is connected in series with aresistor 5 across a source I of alternating current. The coil 9 of arelay ii is connected from one side of the alternating current source 1through a rectifier I3 to the anode 2! of the thyratron 3. A capacitorI5 is connected across the relay coil 9. Terminals I! are provided toimpress a control voltage between the grid IQ of the thyratron and oneterminal of the power source I. A source 2i of biasing voltage may beconnected from the cathode 23 of the thyratron 3 through a grid resistor25 to the grid IQ of the thyratron 3.

In operation, the thyratron 3 is initially nonconductive. The controlvoltage impressed on the grid i9 of the thyratron becomes gradually morepositive to a point at which it is just sufficient to cause thethyratron 3 to become conductive. The thyratron 3 conducts during theremaining portion of the positive half-cycle. A positive half-cycle isdefined as the time during which the source voltage causes the anode 21of the thyratron 3 to be positive with respect to its cathode 23. Whenthe thyratron 3 becomes conductive, current flows from one terminal orthe source I .both through resistor 5 and through the relay coil Bandthe rectifier l3 to the anode 31 of the thyratron 3 and thence to theother terminal of the source "I. The capacitor I5 is charged during thistime. During the negative half cycle no current is flowing through thethyratron 3 and the capacitor partially discharges through the relaycoil. Current flowing from the capacitor causes the relay II to remainclosed during the negative one-half cycle.

During the next positive half-cycle, and before the thyratron 3 becomesconductive, the voltage impressed on its anode is substantially thevoltage of the upper terminal of the power source I. The residualpotential across the relay shunting capacitor l5 does not reduce theimpressed voltage on the anode 2'! of the thyratron 3. Thus, during thesecond positive half-cycle the voltage impressed across the thyratron 3is the same as it was during the previous positive half-cycle and thecontrol voltage is again effective during the positive half-cycle tocause the thyratron 3 to become conductive. During each positive halfcycle, therefore, the voltage impressed across the thyratron 3 is thesame as on all other positive half-cycles and the effect of the controlvoltage on the conductivity of the thyratron remains constant. If thecontrol voltage is sufficient to cause the thyratron 3 to becomeconductive during one positive half-cycle, the same control voltage willbe effective'to cause the thyratron 3 to become conductive during eachsucceeding positive half-cycle and no chattering of the relay willoccur.

I have found that a circuit according to the single figure havingcomponents of the following magnitudes operates satisfactorily:

Capacitor I5, 10 ifd.

Relay ll, coil resistance 1100 ohms operates on Resistor 5, 10,000 ohmsThyratron 3, RCA type Source 1, v.

Rectifier i3, selenium rectifier with rating v.

A. 0. current 50 ma.

No bias voltage 2! was used. I have found that the resistor 5 must havea resistance small with respect to the back resistance of the rectifierH! but the resistance must be large enough not to overload thyratron 3.

Although I have shown and described certain specific embodiment of myinvention, I am fully aware that many modifications thereof are possibleusing the principles herein disclosed. My invention, therefore, is notintended to be restricted to the specific embodiment shown anddescribed.

I claim as my invention:

1. In combination, an electric valve having an anode and acathode, aresistor, circuit means connecting said resistor to the anode of saidelectrio valve, terminals for impressing across said resistor and saidelectric valve in series a voltage, an inductor and a capacitorconnected in parallel, a rectifier connected in series with saidcapacitor and inductor, circuit connections between said resistor andsaid rectifier, capacitor and inductors such that the direction in whichsaid rectifier allows current flow is in the direction from anode tocathode of said electric valve.

2. In combination, an electric valve having an anode and a cathode, animpedance, circuit means connecting said impedance to the anode of saidelectric valve, terminals for impressing across said impedance and saidelectric valve in series a voltage, an inductor and a capacitorconnected in parallel, a rectifier connected in series with saidcapacitor and inductor, circuit connections between said impedance andsaid rectifier, capacitor and inductors such that the direction in whichsaid rectifier allows current flow is in the direction from anode tocathode of said electric valve.

3. In combination, an electric valve having an anode and a cathode, aresistor, circuit means connecting said resistor to the anode of saidelectric valve, terminals for impressing across said resistor and saidelectric valve in series a voltage, an inductor and a capacitorconnected in parallel, an element having a resistance to current flow inone direction substantially different from it resistance to current flowin the other direction connected in series with said capacitor andinductor, circuit connections between said resistor and said element,capacitor and inductors such that the direction in which said elementpresents the least resistance to current flow is in the direction fromanode to cathode of said electric valve.

4. In combination, a coil across which is connected a capacitor, anelectric valve having an anode, a cathode and a control electrode, arectifier, series connections between said coil, rectifier and electricvalve, said rectifier being oriented to conduct current in a directionfrom said anode to said cathode of said electric valve, an impedanceconnected across said rectifier and said coil, terminals for impressingpulsating voltage across said resistor and electric valve, and terminalmeans for impressing a control voltage on said control electrode.

5. In combination, a gaseous discharge device having an anode and acathode, a resistor connected to said anode, connections for applyingalternating current potential across said discharge device and resistorin series, an inductive load device, a capacitor shunting said loaddevice, a rectifier, and means connecting said rectifier in series withsaid load device across said resistor, said rectifier being poled toconduct in the direction from the anode to cathode of said dischargedevice.

6. In combination, a gaseous discharge device having an anode and acathode, an impedance connected in series with said discharge device,connections for applying alternating current potential across saidimpedance and said discharge device; an inductive load device, acapacitor shunting said load device, a uni-directional conducting deviceconnected in series with said inductive load device across saidimpedance, said uni-directional conducting device being poled to conductin the direction of anode to cathode of said discharge device.

GEORGE. W. NAGEL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,870,064 Nickle Aug. 2, 19321,901,628 Brainard Mar. 14, 1933 1,966,077 Nyman July 10, 1934 2,097,578Swart Nov. 2, 1937 FOREIGN PATENTS Number Country Date 557,653 GermanyJuly 19, 1930 528,132 Great Britain Oct. 23, 1940

